Tuesday, February 10, 2009

Pentax DSLR lenses - FF, APS-C, Crop factor...what is what?

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Hi Pentaxian friends.

In the 35mm film era, "non-official" standards of focal length were adopted. All camera makers were more-or-less abiding by these standards. There were the wide-angle lenses, the normal lenses, and the telephoto lenses. The zoom lenses were adopted during the 35mm film era and became standardized as well.

The old school Pentax photographers knew what to expect from a 28mm, a 50mm , a 105mm, a 200mm or a 70-200mm zoom lens. Today's photographers (new school) using the Pentax DSLRs with the APS-C sensor, have to think in terms of actual focal length multiplied by a crop factor of 1.5 to convert the lens to 35mm equivalent. (The terms crop factor was made-up in an attempt to help 35 mm film format photographers understand how their existing ranges of lenses would perform on newly introduced DSLR cameras which had sensors smaller than the 35 mm film format, but often utilized existing 35 mm film format SLR lens mounts. Using an focal length multiplier of 1.5 for Pentax, a photographer might say that a 50 mm lens on his DSLR "acts like" its 50mm has been multiplied by 1.5, by which he means that it has the same field of view as a 75 mm lens on the film camera that he is more familiar with. Of course, the actual focal length of a lens is fixed by its optical construction, and does not change with the format of the sensor that is put behind it.) Manufacturers have continued to produce lenses to the 35mm standards. A 50mm lens is still thought of as a normal lens, but when used with an APS-C sensor, the angle of view is that of a 75mm and thus becomes a better portrait lens, in terms of filling the frame. Listed below are the current line of Pentax lenses, with the 35mm equivalent.

Back to the old school Pentax photographers expecting a 28mm, a 50mm , a 105mm, a 200mm or a 70-200mm zoom lens as he always knew, he would now need the Pentax lens closest to his 35mm equivalent. That would be the DA 21MM F3.2 AL LIMITED = 31.5MM, the DA 35MM F2.8 MACRO LIMITED = 52.5MM, DA 70MM F2.4 LIMITED = 105MM, the D FA 100MM F2.8 MACRO = 150MM, and the DA * STAR 50-135MM F2.8 zoom lens = 75-202.5MM . Of course, using zoom lenses, he could easily get to the focal lengths he is familiar with.

If you get all the current DA* lenses, you can cover 16-300mm or 24-450mm in the 35mm equivalent. Who said Pentax did not have a wide coverage?

I hope this help some of you visualize what the actual angle of view of the current Pentax lenses will be in terms of 35mm equivalent.

Please Note: For the purists and the advanced amateurs and the Pros, the Pentax crop factor is actually 1.53~4 as the actual measurements of the sensor is 23.5mm long x 15.7mm high for the CCD and , 23.4mm long x 15.6 high for the K20D CMOS sensor. For all practical purposes, we are using the 1.5 crop factor as Pentax also use the 1.5 factor for the conversion on their website.